Method and apparatus for the rapid determination of the percentage of carbon in ironand steel



Aug 17 1926. 1,596,615

.J. G. MALMBERG ETAL mmnon AND APPARATUS FOR THE RAPID DETERMINATION OF THE PERCENTAGE OF CARBON IN IRON AND STEEL Filed Feb. 5, 1921 3 Sheets-Sheet 1 Hgh 2 CD yQZQ Aug... 17 1926. 1,596,615.

C. J. G.'MALMBERG ET M. METHOD AND APPARATUS FOR THE RAPID DETERMINATION OF TEE PERCENTAGE OF CARBON IN IRON AND STEEL Filed Feb. 5, 1921 3 Sheets-Sheet 2 4 Try.

Aug. 17 19260 1,596,615

C. J. G. MALMBERG ET AL METHOD AND APPARATUS FOR THE RAPID DETERMINATION OF THE PERCENTAGE OF CARBON IN IRON AND STEEL Filed Feb. 5, 1921 3 Sheets-Sheet 5 Patented Aug. 17, 1926.

UNITED STATES A H 1,596,615 PATENT OFFICE.

CARL J'OHAN GUNNAR MALMBERG, OF SURAHAMMAR, AND JOHAN GUNNAR HOLM- STBDM, 0F SALTSJO-STOBANGEN, SWEDEN.

METHOD AND APPARATUS FOR THE RAPID DETERMINATION OF THE PERCENTAGE OF CARBON IN IBON AND STEEL.

Application filed February 5, 1921, Serial No. 442,895, and in Sweden December 22, 1917.

As generally known the presence of im purities in iron, especially carbon, gives the iron different mechanical as. well as difi'erent magnetic and electrical properties. The presentinvention relates to a method of and apparatus for determining the percentage of carbon in iron specimens, based upon a certain easily measurable magnetic property. It is of very great importance for practical reasons to beable to make this determina tion of the percentage of carbonrapidly and reliably, so that it may be made, for instance in an open-hearth furnace during the process.

The relation between the magnetic prop-.

erties of iron and the percentage of carbon therein is generally known. -Experiments regarding the relation between the magnetic flux and the percentage in carbon of different kinds of steel as well as the changes of the coercive force and the remanence have been made and their results published, but the methods by means of which the percentage of carbon may be inferred from the magnetic properties, are very troublesome, impractical and unreliable. The best method would beto establish the complete magnetic cycle ofthe specimen and to try to make conclusions on that basis, but the measuring is then very troublesome and lengthy and results are impaired by numerous incidental circumstances, which'render it very difiicult to make any conclusions as to the composition of" the specimen. Another known method is that of forging the specimen inthe shape of aring, winding it with insulated copper wire and then by meansof the ballistic method determining the density of the magnetic flux at a certain magnetomotive force or to establish the complete hysteresis loop. In using this method several disturbing factors have'to be eliminated, but such a method cannot be used in practice as it is too lengthy. To use specimens and close the magnetic circuit. by means of yokes (Koepsel s apparatus and others) for determining the magnetic flux density or for establishing the magnetization curve, may of course be done for making comparison of the magnetic properties of different kinds of iron, but such a method is very unreliable for making any conclusions as to the percentage of carbon of the specimen.

The absolute value of the magnetic flux density is dependent on the closing of the magnetic circuit; diflferent specimens give different magnetic leakages at the same magnetomotive force and the same magnetic circuit, and so on. It is evident that these circumstances render a determination of ,the percentage'of carbon impossible, as it can be proved that when the pressure of the yoke on the specimen is varied, difierent values of the flux at the same magnetomotive force and under the same conditions are obtained. I

There 'are more important reasons also why an exact determination of the percentage of carbon of an iron specimen cannot be made on the basis-of the flux density measured against a certain magnetomotive force.

In the course of the assiduous experiments which have resulted in the present invention, it has been found that it is quite another magnetic property of an,iron specimen that is in an exact relation to its percentage of carbon.

, It has been found that when an iron specimenis subjected to the influence of a mag netic field, which is varied several times (to and 'fro) between two values, the definite difl'erence of the magnetic flux indicates the percentage of carbon of. the specimen.

The specimen must be magnetized and 'demagnetized repeatedly between the two chosen values before the difference of the magnetic flux is measured, as it has been found that said difference is constant only after several magnetizations and demagnetizations.

Figure 1 of the annexed drawing shows the mere theoretical fact.

Fig. 2 is a detail View of the apparatus;

Fig. 3 is a sectional view of the device forjmagnetizing and de-magnetizing the specimen, and 4 Fig. 4 is a detail perspective view showing a modified disposition of the magnetic coi The magnetization of the specimen is assumed to be varied between the values H and H of the magnetizing force. To these values correspond then the flux densities I and I stated on the ordinates. According to the present invention neither the value I nor the value I forms the basis for the deapproach gradually be said that the value I-I termination of the percentage of carbon, but

- the difierence between these two values.

ity is obtained only after the specimen has been magnetized and demagnetized several The zigzag line of the diagram is intended to show this progress. The curves an ultimate position. When this position has-been reached it can flux. density of the specimen consists of two portions: a fixed value I and a loose value I I which latter fluctuates with the magnetizing and the demagnetizing between the two magnetizing force values H and H As before stated, experiments have confirmed the fact that'it is this loose value or the magnetic loss in demagnetizing from the field value H to the which can be used as a direct indication of the percentage of carbon.

'It has also been found that it is advantageous with regard to accuracy and rapidity in making thetest that the specimen have pronounced remanent properties. In order to obtain such properties the specimen should be hardened by heating it for a sufficient period at a sufliciently high temperature and then rapidly cooling it.

In practice the magnetic loss between two values of the magnetizing force should be measured by means of a suitable instrument. The constant of the apparatus is determined empirically by measuring the percentage of carbon of a standard specimen. The percentage of carbon can then be read either from a curve or a table or on the scale of the instrument, empiricallygraduated.

The measurement of the magneticloss can of course bemade in various ways, for instance by means of a magnetometer or by the ballistic method. The preferred for practical reasons as the influence of external'magnetic fields then can by the use of a be avoided, for instance moving coil instrument with magnetic circui According to the present method it is possible to measure the percentage of carbon of an iron specimen rapidly and exactly without working the specimen and indeendent of any external magnetic fields and iron objects. A quantity of the melting iron may consequently be taken out of the furnace for making \the specimen. This method enables the decarbonization to be followed and stopped when the percentage of carbon required has been obtained.

There are, as is known, several instruments for measuring the difierenee of the a tightly closed a permanent magnet.

latter method 1s magnetization is magnetic flux of certain iron specimens. However,,1t 18 not possible to use any one of .these instruments directly for determimng the percentage of carbon according to the above .described method. Many incidental circumstances disturb and make it impossible to obtain exactly the same results, for

instance for the same specimen in the same.

apparatus but on difierent occasions. Only after eliminatingor reducing such circumstances to a minimum does the above measuring method become suitable for'technical purposes. The construction of the magnetic measuring instruments is therefore an indispensable complement to the method according to the invention.

As hereinbefore stated, it is necessary that the measuring of 1 -1 may be done rapidly and reliably. The ballistic method must in this regard be considered the best one. The instruments usually used in connection with the method, in which the specimenis inserted in a primary induction coil in which the current flows and an outer secondary coil connected to the ballistic galvanometer, cannot be used partly because the magnetic leakage cannot then be kept constant for the same specimen, neither with closed nor with open magnetic circuits, and partly because the heat produced by the primary current causes changes of temperature which alters the resistance of the secondary coil, and also that of the iron. In the present invention these disturbing factors have been eliminated partly by arranging magnetic screens at the two ends of the iron specimen and thesecondary coil and partly by making the magnetizing and demagnetizmg in an external magnetic circuit relative to the screens either by means of a coil conducting current, or still better, by means of By placing the current coil apart from the specimen, or in a still higher degree by using permanent magnets, the heating disturbances of the pr1- mary current may be eliminated. However, in order to obtain constancy also the variations in the magnetizing pensated. The whole arrangement will, however, be useless if a certain specimen does not give a certain indication. If the effected by means of the primary current coil, 'the current in the secondary coil may cation determined for a constant standard specimen is obtained. however, troublesome. The sources of the current are very frequently not constant. A preliminary adjustment must therefore be made by the aid of an ammeter and thereafter an accurate adjustment by standard. But what is worse, a correcting adjustment must be made during the operaforces' must be com- This adjustment is,

be adjusted until theindij the aid 'of a tion of the instrument on account of the heat after an infinite M wcircuit of the magnet ters the resistance and consequently also the magnetizing current. The more indications made by the instrument the'warmer grows the primary coil and the weaker the magnetizing current. This correction must therefore be made frequently and is tlme consuming, and not fully satisfactory.

As the constancy of the instrument is, as said before, of very great importance, the as well as that of the specimen must be protected against disturbing magnetic fields, which is done by enclosing the apparatus in an Iron box. The magnetic leakage is thus rendered constant in each separate case and changes of the intensity of the ma netic field due to outside influences prevented. I

In the above description of the method it may be pointed out that the curves of magnetization and demagnetization gradually approach their This position is theoretically reached only number of magnetizings, but in practice only a few such magnetizations are required. It is, however, necessary to keep the error, which arises when the magnetizations and demagnetizations are stopped too soon, so small that it does not impair the accuracy of the method. It is therefore always necessary to make prelim- 7 *mary magnetizings in sufficient number he fore the loss is measured. The apparatus must therefore be so constructed that this measurement cannot be ,made unless a certain stated number of magnetizations and demagnetizations have been made. The technical carbometer must therefore include a device which automatically makes these preliminary magnetizations. This is preferably carried out by means of a clockwork.

Carbometers constructed according to the above described invention are shown in Figures 2 to 4.

Figure 2 represents schematically the complete apparatus, and Figure 3 is a detailed view thereof. The apparatus shown in these illustrations consists of "a coil wound with many turns of insulated copper wire 3, a ballistic galvanometer 4 of suitable sensibility and damping, and a devicefor magnetizing and (Fig. 3) between the two magnetizing values chosen for the apparatus.

When the magnetization and the demagnetization is made, in the manner hereinafter described, the coil 2 with the winding 3, in which the specimen is placed, must be furnished with magnetic screens 5 and 6 of soft iron (see Figure 3) in order to obtain constant leakage. The specimen should be cast in a tilted mould in order, to avoid airbubbles. For the same reason the specimen must have rather a largerhead 7 (Fig. 3). When the specimen, hardened as above deultimate position.

on any other portion of the and the contact lever 14.

demagnetizing the specimen 1 scribed, is placed in the coil, it forms an essential part of a magnetic circuit the remaining magnetic resistance is constant. For the purpose of preventing the head of a specimen, which shapes and sizes from exerting any influence uponthe magnetic flux in the circuit, the screens 5 and 6 are inserted. These screens are arranged at such a distance from each other (or the specimen is of such a length) that the cylindrical part of the specimen magnetically connects the plates 5 and 6, while the head 7 is completely outside the one plate.

The ballistic moving coil type. and suitably furnished with a lens movable over the scale for accurate reading of the momentary indication, corresponding to the magnetic loss of the chosen difference in magnetizing forces.

The magnetization and demagnetization may be carried out in different ways.

If an electric current varied between two values is used for'this purpose, the appa ratus may beconstructed as shown in Figure 2. The ends of the magnetic screens 5 and 6 of soft iron, which border the coil 2 in which the specimen is inserted, are connected to a core 8, also made of soft iron, fixed between the ends of the screens. The magnetic circuit is then composed of the specimen, the screen 5, the iron core 8 and the screen 6. This circuit isnow magnetized by sending an electric current from, for instance a storage battery, through the wire 910 wound on the iron core 8 or magnetic circuit. The electric current circuit includes, besides the battery 11 and the wire 9-10, an adjustable rheostat 12, the contact spring On the shaft 18, driven by a clockwork, is fixed a pinion 16. When the clockwork shaft is started and the pinion rotates, the end 17 of the lever 14 is moved upward by the teeth of the pinion 16, making contact-between the lever 14 and the spring 15 by means of the contact 19, once by each tooth of the pinion 16, which passes the end 17 of the lever 14. The current from the batteryv 11 is thus closed and broken also once for each tooth of the said pinion 16. When the contact 19 is shunted by means of the adjustable rheostat 13, the current may also be varied between two certain values determined with the rheostats 12 and 13 instead of being closed and broken. A specimen 1, inserted in the coil '2 is thus magnetized and demagnetized between two definite magnetomotive forces generated by the coil 910 in the magnetic circuit (specimen-pieces 5+86) oncev for each tooth of the pinion 16. As above pointed out, the indication of the magnetic loss in the specimen should be read ofi from the ballistic galvanometer 4 head may have various galvanometer 4 is of usual only not be connected during these preliminary magnetizations, as it would not then be still when the definite reading is to be made. The galvanometer may be connected for instance in the manner shown in Figure 2.

The circuit'from the coil 2 is closed over the outer terminal 29 oi the galvanometer .4, over the outer terminal to the lever 21 and, when the end 25 of this lever is moved UPWHI'd'tO the contact spring 22 and from this spring back to the coil 2. During the preliminary magnetizations the end 24 is not raised, the circuit of the galvanometer is thus broken at the contact pin 28. In order to keep the galvanonieter still damped it is shunted b means of asuitable resistance 31 over t lower spring 23 by the aid "of a pin 27, The lever 21 is raised by the tooth 26 of, the cam 25. This'is effected only-when the definite indication is to be mad e. The cam 25 is for this purpose fixed on the'same shaft-18 as the pinion 16. The clockwork and this shaft 18 are released by pressing a button 44, which acts upon 'a stopping lever fitted with a catch 36. The catch 36 eiig ges the teeth of'the cam 32, also fixed on he shaft 18., 'As will be seem-this cam 32 has only two teeth 33 and .34. .In the original position, (not that shown in the Figure 2), the tooth 34 rests against the catch 36 of the lever 35. The end is then lying behind the tooth has been raised somewhat, the end of the le- 26-and the end of the catch 17, between the teeth 46 and '47. After the iron specimen has been inserted in its lace in the coil 2, the button 44 is presse once. The 'lever 42 which moves on the raised at the end. 41, where it bears the shaft 49 on which the lever 38 is fixed. The spring 40 holds the lever 38 pressed against t e support 39 attached to the arm 42. The- 38 thus moves upward fore end of the lever ly and raises the'end 37 of the lever 35 but only for a moment sufiicient to raise the catch 36 over the tooth 34. When the end 37 ver 38 slides oil? the end 37 when the lever 35 and the catch 36 again fall down on the cam 32. As no tooth now holds the catch 36 the clockwork rotates and the catch 17 is moved up and down once for each tooth of the pin; ion 16- effecting the preliminary magnetizations, as previously described.v After a certain number (in this case 15) of these magnetizations have been made, the clockwork is stopped by the catch 36 on striking the 32. The cams then come shown in the figure.

tooth 33 of the cam into the positions lever 21. These teeth 46 located and the contact' e contact lever 21 and the shaft 43 is thereby vented, at the same time as it ensur s the While the cams are rotating, or after they have been sto ped, the button 44 should be released. 11 releasing this button the lever 38 is pulled back'striking the 'en'd37, so that the lever 38 again slides down below the end 37. and returns to the original position For reading the indication of the galvanometer'4 the button 44 is now pressed once more. Theend 37 is then again raised so that the catch 36 releases the tooth 33 but falls down immediately when the lever 38 passes the end 37, as previously described. On the second pressing of the button 44 the clockwork turns the shaft 18 only part of the way corresponding to the distance between the teeth 33 and 34 of the cam 32.. By this tiirning the tooth 46 operates the lever 14 once and the tooth 26 operates the and 26 are of such a shape and so springs 15 and 22 so placed that the tooth 46 first raises the catch 17 so that the lever 14 on the spring 15 comes into contact by -means of the contact 19. The catch 24 of,

the lever 21 is then immediately raised by the tooth 26, so that the lever 21 and the spring 22 come into contact by the aid of the a contact 28. The catch 17 then falls back from the tooth 46' so that interruption is made at the contact galvanometer 4 then taking place. The catch 24 now falls down from the tooth 26,

breaking the current at the pin 28, but 0108.

ing it at the contact 27. This closing must. take place immediately before the pointer of the alvanomete'r returns from the indication ack to zero. The resistance 31 is in this case so regulated that the motion of the moving coil of the galvanometer is damped or stopped and compels the pointer to stop on zero or close to it. The moment for releasing the button 44 has obviously, nothin to do with this damping. However, after t e button has been released the lever, 38 returns to its original position below the end 37, as before described. By means of such a device which, of course, may be made in many various ways, any chance of oniitting the preliminary magnetizations is presame number of magnetizations always being made.

If the magnetomotive force of the coil 9- -10 is not varied between a certain value and zero, that is, if the primary current is not closed or broken but is varied between two values, that is, if the rheostat 13 is connected in shunt to the contact 19, the rheostat 13 should first be adjusted, so that an ammeter 50 inserted in the shunt, indicates a predetermined value, whereupon the adjustment of the rheostat 12 is made by the aid of a standard, as above described.

However, independently of the method used for magne 'izing and demagnetizing of 13 19, the reading of the 95 and magnetic fluxes through the specimen at,

the specimen, that is, for closing and breaking a magnetic field flowing through the screens 5 and 6 to the specimen, the coil 2- in which the 'loss is induced may be placed on any part of the magnetic circuit. For instance, it may be placed on the screen 6, as shown in Fig. 4. Between the free ends of the screens 5 and 6 a magnetic flux may, as above' described, be introduced or cut off by demagnetizing the. specimen takes place not only in the. specimen itself but also in the screens or the pieces 5 and 6. In view of the magnetic leakage always present the coil 2 should for convenience be placed outside the'pipe 93 in the way shown in F igures 24.

Having no: particularly described the nature of our invention and the manner of its operation, what we claim is:

1. The method of determiningthe percentage of carbon in a specimen'of iron or;

steel which consists in subjecting the specimen to repeated magnetization and demagnetization between two chosen values of the magnetizing force, and measuring the difference between the magnetic fluxes through the specimen at said two values.

2. The method of determining the percentage of carbon in a specimen of iron or steel which consists in hardening the specimen, subjecting the same repeatedly to magnetization and demagnetization between two chosen values of the magnetizing force, measuring the difl'erence between the said two values.

3. Apparatus for determining the percentage of carbon in-a specimen of iron or steel, comprising a magnetic circuit including the specimen to be tested, an induction coil wound upon a portion of said circuit, a magnetizing coil placed on a different portion of said circuit, means for, repeatedly varying the magnetizing forces between "two chosen values, and meansfor measuring the difference between the magnetic fluxes through the specimen at said two values.

4. Apparatus for determining the percentage of carbon in a specimen of iron or steel, comprising a magnetic circuit including the specimen to be tested, an induction coil wound upon said specimen, a magetizing coil placed on a different portion of said circuit, means for repeatedly varying the ence between the magnetic fluxes through the specimen at said two values.

5. Apparatus for determining the percentage of carbon in aspecimen of iron or steel, comprising a magnetic circuit including the specimen to be tested, an induction coil wound. upon a portion of said circuit, and a magnetizing coil placed on a diflerent portion of said circuit, magnetic screens for preventing specimens of different lengths from exerting any influence upon the result and insuring that the same length of specimen is included in the magnetic circuit when the determination is being made.

6. Apparatus for determining the percentage of carbon in a specimen of iron or steel, comprising a magnetic circuit including the specimen to be tested, an induction coil wound upon a portion of said circuit, a magnetizing coil placed on a diflerent portion of said circuit, and an iron box enclosing said circuit for eliminating disturbance due to external magnetic fields and ensuring" constant leakage from the circuit. 7

7. Apparatus for determining the percentage of carbon in a specimen of iron or steel, comprising a magnetic circuit including the specimen to. be tested, an induction coil wound upon a portion of said circuit, a magnetizing coil placed on a diflerent portiontof said circuit,and mechanism for controlling the opening and closing of the cur rent in the magnetizing coil.

8. Apparatus for determining the percentage of carbon in. a specimen 0.15 iron or 'steel, comprising a magnetic circuit includ ing thespecimen to be tested, an induction coil wound upon a portion of said circuit, amagnetizing coil placed on a difi'erent portion of said circuit, and automatically operative mechanism for opening and closing the'current in the magnetizing coil for reln'duction coil, and measuring instrument out and demagnetizing of electrical connection during a predetermined time and automatically operative to connect said measuring instrument and induction coil after said predetermined time. In testimony whereof we have signed our names tothis specification. 1

CARL JOHAN GUNN'AR MALMBERG.

JOHAN GUNNAR noLMsTRoM. 

